New source of greenhouse gas identified

In marine sediments, not only microorganisms but also chemical processes produce nitrous oxide that is harmful to the climate.

In sediments of the Baltic Sea, researchers from Tübingen have identified a previously unknown chemical source of the greenhouse gas nitrous oxide.

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Kordi Vahle/Pixabay; CC0

When scientists talk about greenhouse gases, they convert their effect into CO2 equivalents. In addition to the known carbon dioxide, there are a number of other gases that heat up the climate. Nitrous oxide, also known as laughing gas, is a gas that is around 300 times more harmful to the climate than CO2. Geoscientists at the Eberhard Karls University in Tübingen have now identified a previously unknown source of this greenhouse gas.

Conditions simulated in the laboratory

"Previously, it was assumed that nitrous oxide was mainly created as an intermediate product in the conversion of nitrate by bacteria in typical coastal marine sediments," explains Andreas Kappler. However, measurements had shown more laughing gas than this process could explain. In addition, unexplained nitrous oxide sources were also found in the soils of rice fields and in river sediments. The researchers from Tübingen used sediment samples from the Danish Baltic Sea coast to simulate the conditions in the laboratory and analyze the processes taking place there.

Chemical process forms laughing gas from iron and nitrite

According to the report, chemical processes are responsible for a good quarter of nitrous oxide emissions in marine sediments, rather than microbial processes, as scientists report in the scientific journal "Scientific Reports". "Laughing gas is produced and released extremely quickly," says Caroline Schmidt from the University of Tübingen, describing the observation. However, microorganisms are not completely uninvolved: the starting materials of this reaction - divalent iron and nitrite - are produced by microbes.

Understanding the interaction of microorganisms and sediment chemistry

"The study illustrates how processes on the smallest scale - interactions between microorganisms and sediment chemistry - can have massive effects on global environmental phenomena such as greenhouse gas emissions," Schmidt sums up. The relevance of this issue is made clear by his colleague Kappler: "We must understand all man-made and natural sources of greenhouse gas formation in order to be able to assess future climate developments".